1. Field of the Invention
The present invention relates to a semiconductor device having an organic semiconductor film, and more particularly to an organic thin film transistor having a high driving speed and a high ON/OFF ratio.
All of patents, patent applications, patent publications, scientific articles and the like, which will hereinafter be cited or identified in the present application, will, hereby, be incorporated by references in their entirety in order to describe more fully the state of the art, to which the present invention pertains.
2. Description of the Related Art
The thin film transistor has widely been used as a switching device for a display such as a liquid crystal display. Conventional thin film transistors are made of amorphous or polycrystalline silicon. The formation of the silicon-based thin film transistor needs to use a chemical vapor deposition system which is extremely expensive. The increase in size of the display device including the thin film transistors causes a problem with the transistors causes a problem with the increase in manufacturing cost thereof. The process for depositing or forming the amorphous silicon layer or the polysilicon layer is carried out at an extremely high temperature. Due to this high temperature condition, available materials to the substrate are limited. For example, resin substrates, which are relatively light, are not available.
In order to have solved the above problem, there was proposed the organic thin film transistor using one or more organic materials instead of amorphous silicon or polysilicon. The organic thin film transistor may be formed by vacuum evaporation method or coating method. Those methods make it possible to realize the desired increase in size of the device without any increase in the cost. The temperature necessary in the process for forming the transistor may be relatively low. For those reasons, the organic thin film transistor would be advantageous in less limitation to the available materials, and receive a great deal of expectation for practice.
In recent years, a variety of organic thin film transistor has been reported, for example, by F. Ebisawa et al. in Journal of Applied Physics, vol. 54, p. 3255, 1983; by A. Assadi et al. in Applied Physics Letter, vol. 53, p. 195, 1988; by G. Guillaud et al. in Chemical Physics Letter, vol. 167, p. 503, 1990; by X. Peng et al. in Applied Physics Letter, vol. 57, p. 2013, 1990; by G. Horowitz et al. in Synthetic Metals, vol. 41-43, p. 1127, 1991; by S. Miyauchi et al. in Synthetic Metals, vol. 41-43, 1991; by H. Fuchigami et al. in Applied Physics Letters, vol. 63, p. 1372, 1993; by H. Koezuka et al. in Applied Physics Letter, vol. 62, p. 1794, 1993; by F. Garnier et al. in Science, vol. 265, p. 1684, 1994; by A. R. Brown in Synthetic Metals vol. 68, p. 65, 1994, by A. Dodabalapur et al. in Science vol. 268, p. 270, 1995; by T. Sumimoto et al. in Synthetic Metals vol. 86, p. 2259, 1997; by K. Kudo et al. in Thin Solid Films, vol. 331, p. 51, 1998; K. Kudo et al. Synthetic Metals, vol. 102, p. 900, 1999; and by K. Kudo et al. Synthetic Metals, vol. 111-112, p. 11, 2002.
It has also been known that polymers such as conjugated polymers or thiophenes are available solely or in the form of mixture with other one or more compounds for the organic compound layer in the thin film transistor, as disclosed in Japanese laid-open patent publications Nos. 8-228034, 8-228035, 9-232589, 10-125924, and 10-190001.
It has also been known that metal phthalocyanine compounds are available solely or in the form of mixture with other one or more compounds for the organic compound layer in the thin film transistor, as disclosed in Japanese laid-open patent publication No. 2000-174277.
It has also been known that condensed aromatic hydrocarbons such as pentacene are available solely or in the form of mixture with other one or more compounds for the organic compound layer in the thin film transistor, as disclosed in Japanese laid-open patent publications Nos. 5-55568 and 2001-94107.
Although the research and developments of the organic thin film transistors have been made, the known and conventional organic thin film transistors do not have the required or desired performances because the properties of the compounds used for the organic thin film do not satisfy the requirements. The known and conventional organic thin film transistors are lower in response speed than what is required in practice. The known and conventional organic thin film transistors do not have any practically sufficient ON/OFF ratio. The term xe2x80x9cON/OFF ratioxe2x80x9d means a ratio of a source-drain current in ON-state of the transistor to a source-drain current in OFF-state of the transistor.
In the above circumstances, the development of a novel organic thin film transistor free from the above problems is desirable.
Accordingly, it is an object of the present invention to provide a novel organic thin film transistor free from the above problems.
It is a further object of the present invention to provide a novel organic thin film transistor which exhibits a desired high speed performance and has a high ON/OFF ratio.
The present invention provides an organic thin film transistor. The transistor includes: an organic thin film and first, second and third electrodes. The first and second electrodes are in contact with the organic thin film. The first and second electrodes are separated from each other. The third electrode is separated from the first and second electrodes. The third electrode receives an application of a control voltage which controls a current flowing from one of the first and second electrodes to the other. The organic thin film includes a compound represented by the following general formula [A]:
Xxe2x80x94[xe2x80x94N Ar1Ar2]nxe2x80x83xe2x80x83[A]
where each of Ar1 and Ar2 is selected independently from unsubstituted or substituted aromatic hydrocarbon groups having 6 to 20 carbon atoms and from unsubstituted or substituted aromatic heterocyclic groups having 6 to 20 carbon atoms; and X is selected from unsubstituted or substituted condensed aromatic hydrocarbon groups having 6 to 34 carbon atoms, and the condensed aromatic hydrocarbon groups are monovalent, divalent, trivalent or tetravalent groups; and n is the natural number in the range of 1-4.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.